Download Chapter 2: Integers & Introduction to Solving Equations

Section 2.2
Adding Integers
To Add Two Numbers with the Same Sign
End
Start
2+3= 5
2
-6 -5 -4 -3 -2 -1
End
0
1
Start
-3
0
0
2
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5
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-2 + (-3) = -5
-2
-6 -5
-5 -4
-4 -3
-3 -2
-2 -1
-1
-6
3
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1
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2
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To Add Two Numbers with the
Same Sign
Step 1. Add their absolute values.
Step 2. Use their common sign as the sign
of the sum.
Examples:
-3 + (-5) = -8
5+2=7
Martin-Gay, Prealgebra, 5ed
3
To Add Two Numbers with Different Signs
2 + (-3) = -1
-3
End
Start
2
0
1
-6 -5 -4 -3 -2 -1
3
3
4
5
6
End
-2 + 3 = 1
-2 Start
-6 -5 -4 -3 -2 -1
2
0
1
2
3
4
5
6
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To Add Two Numbers with
Different Signs
Step 1. Find the larger absolute value
minus the smaller absolute value.
Step 2. Use the sign of the number with
the larger absolute value as the
sign of the sum.
Examples:
-4 + 5 = 1
6 + (-8) = -2
Martin-Gay, Prealgebra, 5ed
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Helpful Hint
If a is a number, then
-a is its opposite.
a + (-a) = 0
-a + a = 0
The sum of a number
and its opposite is 0.
Martin-Gay, Prealgebra, 5ed
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Helpful Hint
Don’t forget that addition is
commutative and associative. In
other words, numbers may be added
in any order.
Martin-Gay, Prealgebra, 5ed
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Evaluating Algebraic
Expressions
Evaluate x + y for x = 5 and y = -9.
Replace x with 5 and y with -9 in x + y.
x + y = ( 5 ) + ( -9)
=-4
Martin-Gay, Prealgebra, 5ed
8